Gas leak valve

ABSTRACT

A gas leak valve is provided that uses a hollow, porous-wall, closed-end tube communicating with the gas to be metered and slidable past a vacuum seal so as to expose more or less of the porous tube wall to the vacuum region and hence to controllably leak the gas through the porous wall into the vacuum system.

United States Patent 1 Veach et al.

[ GAS LEAK VALVE [75] Inventors: Allen M. Veach; William A. Bell, Jr.,

both of Oak Ridge, Tenn.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission, Washington, D.C.

[22] Filed: Dec. 1, 1971 [21] Appl. No.: 203,747

[52] US. Cl. 138/46, 251/121 [51] Int. Cl. F15d 1/00 [58] Field ofSearch 138/46, 40, 44, 45, 138/37, 41, 42, 43; 251/121 [56] ReferencesCited UNITED STATES PATENTS 3,338,548 8/1967 Mott 138/43 VA CU U M [1113,738,392 June 12, 1973 3,042,079 7/1962 Swift et a1 138/42 2,887,1295/1959 Stear 138/43 2,118,830 5/1938 Veenschoten 251/133 X PrimaryExaminerGeorge E. Lawrence Assistant Examiner-Steven PollardAttorney-Roland A. Anderson [57] ABSTRACT A gas leak valve is providedthat uses a hollow, porouswall, closed-end tube communicating with thegas to be metered and slidable past a vacuum seal so as to expose moreor less of the porous tube wall to the vacuum region and hence tocontrollably leak the gas through the porous wall into the vacuumsystem.

2 Claims, 3 Drawing Figures was 1 m g Pmmmw'zm INVENTORS. Allep M. VeachBY William A. Bell, Jr.

ATTORNEY.

PAIENTEB 4 3.738.392

SIIE EIT a a? 2 45psi 28 FLOW RATE (cc/min) 25psi 14.7psi

I I 20 40 6O 8O REGULATINE CYLINDER EXPOSED LENGTH Imm) Fig.2

8 ROTATION (TURNS) 6- I l I l I I I l 2 4 6 8 10 I2 I4 16 I8 FLOW RATE(cc/min) Fig.3

INVENTORS. Aljep M. Veach BY WIIIIamABeII, Jr. 4

ATTORNEY;

BACKGROUND OF THE INVENTION This invention was made in the course of, orunder, a contract with the U. S. Atomic Energy Commission.

Many principles have been incorporated into the construction of variousvalves designed to control the rate of leakage of gaseous products intoa vacuum system. The number of valve designs available attests, to somedegree, to the difficulty experienced in achieving a universal valve.Most prior art valves are rendered inoperative by corrosive gases, andnearly all are relatively complicated and expensive. In general, suchleak valves operate on the principle of withdrawal of a needle from anorifice, of separatingtwo mating surfaces, of vibrating one of twomating surfaces, or of restricting the cross section of a long elasticpassage. Typically, the response of prior art gas leak valves isnon-linear at low flow rates. Thus, there exists a need for an improvedgas leak valve that has a substantially linear response for all flowrates at a given pressure. The present invention was conceived to meetthis need in a manner to be described hereinbelow.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide an improved gas leak valve that has a substantially linearresponse for all flow rates at any given input pressure for the inputgas. This object has been accomplished in the present invention byproviding a sliding, hollow, cylindrical member of porous material as acontrol device within a corrosion resistant guide cylinder. This porousmember is provided with a solid end and is adapted to pass through adouble O-ring system which serves as a leak-tight trap for the movementof the porous member into a vacuum region and as a barrier to separatethe low pressure (vacuum) side of the system from the pressure withinthe enclosing corrosion resistant guide cylinder on the other side ofthe system in a manner to be described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional drawing ofthe valve of the present invention;

FIG. 2 is a graph showing typical results obtained with the valve'ofFIG. I; and

FIG. 3 is a graph showing the response of a typical commercial leakvalve.

DESCRIPTION OF THE PREFERRED EMBODIMENT As illustrated in FIG. 1, thegas leak valve of the present invention utilizes a sliding hollow,cylindrical member 19 of porous material as a control device within acorrosion resistant (nylon, Teflon, etc.) guide cylinder 17. The chamberof guide cylinder 17 is sealed to prevent gas leakage into thesurrounding atmosphere by a guide ring 23 and its associated O-ring. Ametallic gas feed tube is mounted in the guide ring 23, as well as theporous member 19 on opposite sides thereof, as shown, and the gas feedtube 15 communicates with the interior of the porous member 19 by meansof feedthrough hole in the guide ring 23.

A high pressure gas to be leaked into the vacuum region enters the tube15 at a point 16 from a source of gas supply, not shown. Gas feed tube15, which also serves as a push rod, is affixed to a member 25 and the 2tube 15 is driven into the guide cylinder 17 by means of a smallreversible motor, not shown, by means ofa worm drive 18 feeding throughthe affixed member 25. The porous, hollow member 19 may be constructedfrom graphite, for example, and it is provided with a solid end 21. Theinside pressure of the porous member 19 is the same as and communicateswith that in the push rod 15. The porous graphite tube 19 is allowed topass into and through a double O-ring system 20 and 22, which serves asa leak-tight trap for the movement of tube 19 and as a barrier toseparate the low pressure (vacuum) side of the system from the pressurein the guide cylinder 17.

The amount of gas from the high pressure region inside graphite tube 19that is allowed to leak into the low pressure cylinder 24 is a functionof the surface area of the porous graphite tube 19 which is exposed tothe low pressure side (if other parameters are fixed). The gas leakedinto the cylinder 24 is fed into the vacuum system by means of anopening26 mounted in the end of cylinder 24 and communicating therewith. Toincrease the flow rate, the metal push rod 15 is inserted further intothe low pressurecylinder 24 by the reversible motor; to decrease theflow rate, the rod 15 is withdrawn a desired amount from this region. Tostop the flow completely, the rod 15'is withdrawn until the solid end I21 0f the graphite tube 19 passes into the O-ring 20.

Four leak-rate curves, as shown in FIG. 2, were obtained by makingincremental changes in the length of the porous tube 19 exposed to lowpressure in the operation of the device of FIG. 1. It should be notedthat the data for plotting the four response curves in FIG. 2 were suchthat thecurves were substantially linear, and have been shown as suchfor the sake of clarity. The graphite tube 19 was moved a total distanceof 73 mm, thus changing the exposed area from 0 to 945 mm The outsideparameters in the four determined curves were, respectively, (a) 14.7psi air, (b) 25 psi argon, (c) 35 psi argon, and (d) 45 psi argon.Adjustments in exposed tube 19 length were made by the small reversiblemotor with a speed of 6 rpm. With this system, 30 seconds were requiredfor each 3.5 mm of travel. The slope of rate-with-area response is seento vary, as expected, with the applied pressure.

In FIG. 3, the response of a commercially available leak valve is shown.The non-linearity at low flow rates is typical for such valves.

The gas leak valve described above will be used in the ElectromagneticIsotopes Separations Program at one of the U. S. Governmentlaboratories. It provides the vacuum via the porous member (uniquefeature not" shown to exist with other type valves).

6. Minimizes construction costs and problems of re pair due to wear orcorrosion.

In addition to isotope separation, the leak valve of V the presentinvention could also have application in" vacuum instrumentation, highenergy accelerators, and" allied technology.

position of the sliding.

The present gas leak valve was designed for simplicdesign can producealmost any leak response desired while providing additionally for theentrance of filtered gas into the system without its contacting anylubricants.

The following modifications are within the scope of the presentinvention:

1. Increased sensitivity in linearresponse of flow rate with position(thinner walls or increased pressure on the high-pressure side of theporous member);

2. Decreased sensitivity in linear response with position, when such isdesired (thicker walls or decreased pressure on the high-pressure sideof the porous member); and

3. Non-linear leak response with position, when such is desired(conical-shaped or otherwise contoured interior walls of sliding porousmember).

This invention has been described by way of illustration rather thanlimitation and it should be apparent that it is equally applicable infields other than those described.

What is claimed is:

1. An improved gas leak valve comprising a hollow, porous-wall tubeprovided with a solid closed end and an open end; a gas-feed tube; aguide ring, said gas-feed tube affixed to said open end of saidporous-wall tube and communicating therewith by means of said guidering, said gas-feed tube acting as a push-rod for said porous-wall tube;a guide cylinder provided with an open end with the other end thereofdefining a passageway for movement of said porous-wall tubetherethrough, said guide cylinder enclosing a portion of saidporous-wall tube and a portion of said gas-feed tube; a sealing-O-ringpositioned between said guide ring and the inner surface of said guidecylinder; a low-pressure cylinder adapted to be positioned within avacuum chamber and provided with a gas-leak aperture on one end thereof;and a double O-ring sealing system encompassing saidporous tube andbeing affixed to the other end of said low-pressure cylinder and to saidother end of said guide cylinder, said porous tube being adapted to bepositioned by said push-rod gas-feed tube from a no flow position todesired and selected further positions within said low-pressure cylinderto thereby selectively control the flow rate of feed gas from saidgasfeed tube and then through said porous-wall tube into saidlow-pressure cylinder for exit through said gas-leak aperture as afunction of the degree of insertion of said porous-wall tube into saidlow-pressure cylinder past said double O-ring sealing system.

2. The gas leak valve set forth in claim 1, wherein said porous-walltube is fabricated from graphite.

1. An improved gas leak valve comprising a hollow, porous-wall tubeprovided with a solid closed end and an open end; a gas-feed tube; aguide ring, said gas-feed tube affixed to said open end of saidporous-wall tube and communicating therewith by means of said guidering, said gas-feed tube acting as a push-rod for said porous-wall tube;a guide cylinder provided with an open end with the other end thereofdefining a passageway for movement of said porous-wall tubetherethrough, said guide cylinder enclosing a portion of saidporous-wall tube and a portion of said gas-feed tube; a sealing O-ringpositioned between said guide ring and the inner surface of said guidecylinder; a low-pressure cylinder adapted to be positioned within avacuum chamber and provided with a gas-leak aperture on one end thereof;and a double O-ring sealing system encompassing said porous tube andbeing affixed to the other end of said low-pressure cylinder and to saidother end of said guide cylinder, said porous tube being adapted to bepositioned by said push-rod gas-feed tube from a no flow position todesired and selected further positions within said lowpressure cylinderto thereby selectively control the flow rate of feed gas from saidgas-feed tube and then through said porouswall tube into saidlow-pressure cylinder for exit through said gas-leak aperture as afunction of the degree of insertion of said porous-wall tube into saidlow-pressure cylinder past said double O-ring sealing system.
 2. The gasleak valve set forth in claim 1, wherein said porous-wall tube isfabricated from graphite.